Disc brakes in which the rotational movement of an input shaft is converted into a sliding movement of a plate so as to push a piston bearing one of the brake pads is known. An adjuster for compensating for pad wear is inserted between the plate and the piston. It for example comprises a push-rod forming a screw/nut assembly able to increase its length automatically in response to pad wear. Actuation of the shaft by means of the parking brake lever handle causes mechanical application of the brakes. Furthermore, the piston defines, with the brake caliper, a chamber of fluid such that fluid pressure on the piston through actuation of the brake pedal and by means of the hydraulic circuit causes the piston to slide in order to apply the brakes.
In such a brake, most of the parts able to transmit mechanical force to the piston in the case of operation of the brake are bathed in the chamber of fluid. In addition, in the event of braking being commanded via the hydraulic circuit, the pressure is applied to the piston and displaces it, driving certain parts of the mechanical connection along with it. More specifically, a first part of the moving gear follows the piston until the wear compensating pushrod extends, then, as the latter forms a pressure sensor, it is all of the moving gear which moves. In consequence, some of the energy of the fluid is wasted on moving parts whose movement makes no contribution to the actual braking effort.